netdev - [PATCH v3 net-next 01/10] net/sched: taprio: don't access q->qdiscs[] in unoffloaded mode during attach()

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Date: Tue,  1 Aug 2023 21:24:12 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	Jiri Pirko <jiri@...nulli.us>,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>,
	linux-kernel@...r.kernel.org,
	intel-wired-lan@...ts.osuosl.org,
	Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@...el.com>,
	Peilin Ye <yepeilin.cs@...il.com>,
	Pedro Tammela <pctammela@...atatu.com>,
	Richard Cochran <richardcochran@...il.com>,
	Zhengchao Shao <shaozhengchao@...wei.com>,
	Maxim Georgiev <glipus@...il.com>
Subject: [PATCH v3 net-next 01/10] net/sched: taprio: don't access q->qdiscs[] in unoffloaded mode during attach()

This is a simple code transformation with no intended behavior change,
just to make it absolutely clear that q->qdiscs[] is only attached to
the child taprio classes in full offload mode.

Right now we use the q->qdiscs[] variable in taprio_attach() for
software mode too, but that is quite confusing and avoidable. We use
it only to reach the netdev TX queue, but we could as well just use
netdev_get_tx_queue() for that.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
v1->v3: none

 net/sched/sch_taprio.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index 717ae51d94a0..d9ff75a08e12 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -2134,14 +2134,20 @@ static void taprio_attach(struct Qdisc *sch)
 
 	/* Attach underlying qdisc */
 	for (ntx = 0; ntx < dev->num_tx_queues; ntx++) {
-		struct Qdisc *qdisc = q->qdiscs[ntx];
+		struct netdev_queue *dev_queue = netdev_get_tx_queue(dev, ntx);
 		struct Qdisc *old;
 
 		if (FULL_OFFLOAD_IS_ENABLED(q->flags)) {
+			struct Qdisc *qdisc = q->qdiscs[ntx];
+
 			qdisc->flags |= TCQ_F_ONETXQUEUE | TCQ_F_NOPARENT;
-			old = dev_graft_qdisc(qdisc->dev_queue, qdisc);
+			old = dev_graft_qdisc(dev_queue, qdisc);
 		} else {
-			old = dev_graft_qdisc(qdisc->dev_queue, sch);
+			/* In software mode, attach the root taprio qdisc
+			 * to all netdev TX queues, so that dev_qdisc_enqueue()
+			 * goes through taprio_enqueue().
+			 */
+			old = dev_graft_qdisc(dev_queue, sch);
 			qdisc_refcount_inc(sch);
 		}
 		if (old)
-- 
2.34.1